Prior to 1997 the assignee of this invention has manufactured and sold commercially toner cartridges of two different general designs. For its larger laser printers the cartridge has contained a pump to meter toner of the kind disclosed in U.S. Pat. Nos. 5,012,289 to Aldrich et al. and 5,101,237 to Molloy, while the external structure of the cartridge is as disclosed in U.S. Pat. No. 5,136,333 to Craft et al. Details of other elements in the cartridge have varied.
For a smaller, light emitting diode printer, the cartridge is as disclosed in U.S. Pat. No. 5,337,032 to Baker et al., which has a toner hopper extending well below a level having the toner adder roller and which has independent driven systems for the photoconductor roller and for the developer roller system as disclosed in U.S. Pat. No. 5,331,378 to Baker et al.
Cartridges are typically located by elements on their cover or frame, not directly based on the location of photoconductor. In 1997 the assignee of this invention began selling a printer with cartridge having the shaft of the photoconductor drum as the primary locator and a flat ledge opposite for resting on a roller member in the printer. This cartridge contains a photosensitive roller, the central shaft of which extends unobstructed to be contacted by the printer as a vertical and front to rear locator. A hopper and developer roller assembly is attached to the cartridge cover assembly through a spring force. The cartridge cover assembly has elongated surfaces to receive a downward pressing member from the printer. The hopper and developer roller assembly has flat ledges to ride on rollers in the printer thereby permitting adjustment of the contact between the photosensitive roller and the developer roller. A cover assembly integral with the photoconductive roller has a locating surface near the hopper which rests on the frame of the printer positively locating the photoconductive roller.
The two front support wheels which define the plane of lateral movement between the two assemblies are in the printer, with a flat surface on the hopper to receive these rollers. Since the under side of the developer unit is part of the media path, referencing the hopper assembly to the printer improves location accuracy of the media path. The cartridge is resistant to rough handling. A minor advantage is that the cost of the wheels and their installation is eliminated from the cartridge.
The photosensitive roller is integral with a gear with teeth. These teeth mesh with a gear from the printer. Other mechanisms in the cartridge are separately driven. However, a photosensitive roller is subject to forces from a paper or other media which are pulled across the roller to transfer the toner image. Another influence is the developer roller, which has a nip contact to the photosensitive roller and a higher tangential velocity.
The photosensitive roller experiences drag from the cleaner blade. However, during use the wear of the cleaner blade results in the drag dropping greatly. Other drag forces, such as at the bearings, are very small.
Paper contacting the photosensitive roller is being pulled by the fixing station while the trailing part of the paper is still in contact with the photosensitive drum. Wrinkle-free paper handling often results in tension from the fuser roller that may be significant.
The effects of low inherent drag on the photosensitive roller, an incidental driving force from the developer roller, and the pull from the fuser roller nip, alone or in combination, can result in imprecise and wavering rotation of the photosensitive roller (termed "jitter"). The teeth between the input gear of the photosensitive roller and the drive gear may actually separate tangentially, resulting in quite apparent distortion of the printed image. Additionally, since pressure at the teeth tends to physically flatten surface defects, loss of such pressure results in some loss of precise rotation and consequent impairment of the printed image.
This invention applies a highly uniform frictional drag to the photosensitive drum. A spring clutch operating in the unwind direction applies such a drag and is so employed. Uniform response is also achieved by having grease at the friction surface. Where drag is produced by lateral movement of two contacting surfaces, the friction characteristics of the grease provide uniform drag. In all cases the grease promotes consistent, smooth operation.